Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $208.76   8.864%   $227.2645   $227.26   $227.25   $227.30  
  Purchase #2 $58.38   5.844%   $61.7917   $61.79   $61.80   $61.80  
  Purchase #3 $215.59   9.762%   $236.6359   $236.64   $236.65   $236.60  
  Purchase #4 $249.47   7.225%   $267.4942   $267.49   $267.50   $267.50  
  Purchase #5 $11.59   7.186%   $12.4229   $12.42   $12.40   $12.40  
  Purchase #6 $193.85   10.844%   $214.8711   $214.87   $214.85   $214.90  
  Purchase #7 $191.99   5.244%   $202.058   $202.06   $202.05   $202.10  
  7 purchase totals = $1,129.63       $1,222.5383   $1,222.53   $1,222.50   $1,222.60